The present invention relates to the lubrication of a pin-mounted rocker tip roller, and in particular to bearing oil slots in the pin which supply lubricant to and clear debris from between the pin and roller.
Rocker tip rollers have long been used in long-life combustion engines to transfer the rocking motion of a rocking member to a linear motion member, without imposing side loads, and with minimal wear between the members. Rocker tip rollers require lubrication at the roller/pin interface, to facilitate the rather limited roller rotation about the pin which is induced by relative motion between the rocking member and linear motion member. The limited roller rotation and point or line contact by the roller are what produce linear motion in the linear motion member, without side loading and with minimal friction wear. Longer life operation is thereby enjoyed in engines which use rocker tip rollers.
In combustion engines, a rocker tip roller is typically incorporated into one end of a rocker arm and contacts the end of a valve stem to produce linear motion at the valve. Typically, the rocker tip roller is mounted on a pin and may include a bushing between the pin and roller. Lubrication is most often provided by lubricating oil applied at the roller/pin interface, and the oil penetrates into the interface. When pressure is applied to the rocker tip roller and causes the roller to roll relative to the pin, a squeeze film develops at the interface and oil squeezes out axially along the pin. Although oil again migrates into the interface when the pressure is reduced, it has been found that the center of the roller/pin interface is typically starved for oil so that a complete squeeze film does not form, increasing friction wear. The limited amount of oil available to penetrate to the center of the interface contributes to this problem.
In addition, it has been found that debris manages to find its way into the roller/pin interface, causing damage to the pin and roller surfaces, and where used, to the bushing surfaces. The grooving, abrasion and increased friction at the roller/pin or bushing/pin interface can result in premature and sudden failure of the engine.
Accordingly, the need exists for improved lubrication of rocker tip roller lubrication to prevent failure and improve the longevity of such elements in engines designed for long-life performance.